Semiconductor device and method for producing the same

ABSTRACT

Provided, is a reliable semiconductor device with a layered interconnect structure that may develop no trouble of voids and interconnect breakdowns, in which the layered interconnect structure comprises a conductor film and a neighboring film as so layered on a semiconductor substrate that the neighboring film is contacted with the conductor film. In the device, the materials for the conductor film and the neighboring film are so selected that the difference between the short side, a p , of the rectangular unit cells that constitute the plane with minimum free energy of the conductor film and the short side, a n , of the rectangular unit cells that constitute the plane with minimum free energy of the neighboring film, {|a p −a n |/a p}×100=A (%) and the difference between the long side, b   p , of the rectangular unit cells that constitute the plane with minimum free energy of the conductor film and the long side, b n , of the rectangular unit cells that constitute the plane with minimum free energy of the neighboring film, {|b p −b n |/b p}×100=B (%) satisfy an inequality of {A+B×(a   p /b p )}&lt;13. In this, the diffusion of the conductor film is retarded.

This application is a Divisional application of application Ser. No.11/392,540, filed Mar. 30, 2006, which is a Continuation application ofapplication Ser. No. 10/878,018, filed Jun. 29, 2004, now U.S. Pat. No.7,030,493, issued Apr. 18, 2006, which is a Continuation application ofapplication Ser. No. 09/985,904, filed Nov. 6, 2001, now abandoned,which is a Continuation application of application Ser. No. 09/255,856,filed Feb. 23, 1999, now U.S. Pat. No. 6,989,599, issued Jan. 24, 2006,the contents of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device, in particular,to that with a layered interconnect structure.

In recent large-scale-integration, high-performance semiconductordevices, copper (Cu) interconnects are being employed as having lowerelectric resistance than conventional aluminum (Al) interconnects.However, diffusion of copper (Cu) atoms into silicon (Si) substrates orinsulating films will detract from the characteristics of the devices.To prevent the copper (Cu) diffusion, a diffusion barrier is formedadjacent, to the copper (Cu) film. As the material for the diffusionbarrier, high-melting-point metal films of, for example, titaniumnitride (TiN), tungsten (W) or tantalum (Ta) have been investigated, asin the Nikkei Microdevice (for July 1992, pp. 74-77).

Large-scale-integration semiconductor devices with fine patterns receivehigh-density current, in which, therefore, atoms are diffused owing toelectron streams flowing therein and to heat as generated by the flow tocause voids and interconnect breakdowns. The problem with the devices isso-called electromigration. As compared with aluminum (Al) films, copper(Cu) films, as having a higher melting point, are difficult to diffuse,and are therefore expected to have good electromigration resistance.However, layered interconnect structures in which a diffusion barrierof, for example, a titanium nitride (TiN) film, a tungsten (W) film or atantalum (Ta) film is kept in contact with a copper (Cu) film could nothave satisfactory electromigration resistance, and therefore often posethe problem of voids and interconnect breakdowns.

SUMMARY OF THE INVENTION

Given that situation, the object of the invention is to provide areliable semiconductor device with a layered interconnect structure thatmay develop no trouble of voids and interconnect breakdowns.

We, the present inventors have clarified that, in a layered interconnectstructure where a diffusion barrier of, for example, a titanium nitride(TiN) film, tungsten (W) film or a tantalum (Ta) film is kept in contactwith a copper (Cu) film, the significant difference between the materialof the diffusion barrier material and copper (CU) in the Length of thesides of the unit cell brings about disordered atomic configuration inthe interface therebetween thereby promoting copper diffusion thatresults in the trouble of voids and interconnect breakdowns. Therefore,in order to prevent the voids and breakdowns in copper (Cu)interconnects, a material that differs little from copper (Cu) in thelength of the sides of the unit cell shall be used for the film to bedisposed adjacent to the copper (Cu) film thereby inhibiting the copperdiffusion. We have further clarified that, in a layered interconnectstructure comprising a conductor film and a neighboring film as layeredadjacent to the conductor film, when the difference between the shortside, a_(p), of the rectangular unit cells that constitute the planewith minimum free energy of the conductor film and the short side,a_(n), of the rectangular unit cells that constitute the plane withminimum free energy of the neighboring film, {|a_(p)−a_(n)|/a_(p)}×100=A(%), is smaller than 13% and when the difference betweoen the long-side,b_(p), of the rectangular unit cells that constitute the plane withminimum free energy of the conductor film and the long side, b_(n), ofthe rectangular unit cells that constitute the plane with minimum freeenergy of the neighboring film, {|a_(p)−a_(n)|/a_(p)}×100=B (%), asmultiplied by (a_(p)/b_(p)), iis smaller than 13, then the diffusion ofthe conductor film is retarded to prevent voids and interconnectbreakdowns. In addition, we have still further clarified that,especially when A and B satisfy an inequality of {A+B×(a_(p)/b_(p))}<13,preferred results are obtained. The definitions of the short side, a,and the long side, b, in rectangular unit cells as referred to hereinare illustrated in FIG. 6.

Therefore, the object of the invention noted above is attained by asemiconductor device with a layered interconnect structure comprising aconductor film and a neighboring film as so layered on a semiconductorsubstrate that the neighboring film is contacted with the conductorfilm, wherein the materials for the conductor film and the neighboringfilm are so selected that the difference between the short side, a_(p),of the rectangular unit cells that constitute the plane with minimumfree energy of the conductor film and the short side, a_(n), of therectangular unit cells that constitute the plane with minimum freeenergy of the neighboring film, {|a_(p)−a_(n)|/a_(p)}×100=A (%) and thedifference between the long side, b_(p), of the rectangular unit cellsthat constitute the plane with minimum free energy of the conductor filmand the long side, b_(n), of the rectangular unit cells that constitutethe plane with minimum free energy of the neighboring film,{|b_(p)−b_(n)|/b_(p)}×100=B (%) satisfy an inequality of{A+B×(a_(p)/b_(p))}<13.

The object is also attained by a semiconductor device with a layeredinterconnect structure comprising a copper (Cu) film and a neighboringfilm as so layered on a semiconductor substrate that the neighboringfilm is contacted with the copper (Cu) film, wherein the neighboringfilm is any of a rhodium (Rh) film, a ruthenium (Ru) film, an iridium(Ir) film, an osmium (Os) film or a platinum (Pt) film.

The object is also attained by a semiconductor device with a layeredinterconnect structure comprising a platinum (Pt) film and a neighboringfilm as so layered on a semiconductor substrate that the neighboringfilm is contacted with the platinum (Pt) film, wherein the neighboringfilm is any of a rhodium (Rh) film, a ruthenium (Ru) film, an iridium(Ir) film or an osmium (Os) film.

Concretely, preferred embodiments of the invention are as follows:

A semiconductor device with a layered structure comprising a copper (Cu)film interconnect formed on one primary surface of a semiconductorsubstrate, and a diffusion barrier formed in contact with the copper(Cu) film interconnect, wherein the diffusion barrier is of a ruthenium(Ru) film, and the copper (Cu) film interconnect has a layered structurecomprising a copper (Cu) film as formed through sputtering and a copper(Cu) film as formed through plating.

A semiconductor device with a layered structure comprising a copper (Cu)film interconnect formed on one primary surface of a semiconductorsubstrate, and a diffusion barrier formed in contact with the copper(Cu) film interconnect, wherein the diffusion barrier is of a ruthenium(Ru) film, and the copper (Cu) film interconnect has a layered structurecomprising a copper (Cu) film as formed through physical vapordeposition (PVD) and a copper (Cu) film as formed through chemical vapordeposition (CVD).

A semiconductor device with a layered structure comprising a copper (Cu)film interconnect formed on one primary surface of a semiconductorsubstrate, and a diffusion barrier formed in contact with the copper(Cu) film interconnect, wherein the diffusion barrier is of asputter-deposited ruthenium (Ru) film, and the copper (Cu) filminterconnect has a layered structure comprising a copper (Cu) film asformed through sputtering and a copper (Cu) film as formed throughplating or chemical vapor deposition (CVD).

A semiconductor device with a structure comprising a copper (Cu) filminterconnect formed on one primary surface of a semiconductor substrate,and a plug form ed in contact with the copper (Cu) film interconnect,wherein the plug is of at least one film selected from the groupconsisting of a rhodium (Rh) film, a ruthenium (Ru) film, an iridium(Ir) film, an osmium (Os) film and a platinum (Pt) film, and at leastone of the copper (Cu) film interconnect and the plug contains a layeras formed through physical vapor deposition (PVD).

A semiconductor device with a structure comprising a copper (Cu) filminterconnect formed on one primary surface of a semiconductor substrate,a diffusion barrier formed in contact with the copper (Cu) filminterconnect, and a plug formed in contact with the diffusion barrier,wherein the diffusion barrier is of a ruthenium (Ru) film, the plug isof a ruthenium (Ru) film, and at least one of the copper (Cu) filminterconnect and the plug contains a layer as formed through physicalvapor deposition (PVD).

A semiconductor device with a structure comprising a copper (Cu) filminterconnect formed on one primary surface of a semiconductor substrate,a first diffusion barrier formed in contact with the copper (Cu) filminterconnect, a plug formed in contact with the first diffusion barrier,and a second diffusion barrier formed in contact with the plug and thefirst diffusion barrier, wherein the first diffusion barrier is of aruthenium (Ru) film, the plug is of a ruthenium (Ru) film, the seconddiffusion barrier is of a titanium nitride (TiN) film, and at least oneof the copper (Cu) film interconnect and the first diffusion barrier isof a film as formed through sputtering.

A semiconductor device with a structure comprising a platinum (Pt)electrode film formed on one primary surface of a semiconductorsubstrate, and a neighboring film formed in contact with the platinum(Pt) electrode film, wherein the neighboring film is at least one filmselected from the group consisting of a rhodium (Rh) film, a ruthenium(Ru) film, an iridium (Ir), film and an osmium (Os) film, and at leastone of the platinum (Pt) electrode film and the neighboring film is of afilm as formed through sputtering.

A method for producing semiconductor devices, which comprises thefollowing steps:

a step of forming a ruthenium (Ru) film on,one primary surface of asemiconductor substrate through sputtering;

a step of forming a first copper (Cu) film to be in contact with theruthenium (Ru) film, through sputtering; and

a step of forming a second copper (Cu) film to be in contact with thefirst copper (Cu) film, through plating or chemical vapor deposition(CVD).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a layered interconnectstructure of a semiconductor device of the first embodiment of theinvention;

FIG. 2 is a graph indicating the effect of neighboring film materials ona conductor film of copper (Cu), relative to the diffusion coefficientof the copper (Cu) film;

FIG. 3 is a characteristic curve indicating the effect of neighboringfilm materials on a conductor film of copper (Cu), relative to thediffusion coefficient of the copper (Cu) film along the dotted line inFIG. 2;

FIG. 4 is a characteristic graph indicating the effect of neighboringfilm materials on a conductor film of platinum (Pt), relative to thediffusion coefficient of the platinum (Pt) film;

FIG. 5 is a characteristic curve indicating the effect of neighboringfilm materials on a conductor film of platinum (Pt), relative to thediffusion coefficient of the platinum (Pt) film along the dotted line inFIG. 4;

FIG. 6 is a view showing the atomic configuration in rectangular unitcells, and the short side and the long side of each unit cell;

FIG. 7 is a cross-sectional view showing a layered interconnectstructure of a semiconductor device of the second embodiment of theinvention;

FIG. 8 is a cross-sectional view showing the principal part of asemiconductor device of the third embodiment of the invention; and

FIG. 9 is a cross-sectional view showing the principal part with apreferred functional structure of a semiconductor device of the thirdembodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Embodiments of the invention are described hereinunder with reference tothe drawings.

First referred to is FIG. 1, which shows a cross-sectional structure ofthe layered interconnect structure part of a semiconductor device of thefirst embodiment of the invention.

As in FIG. 1, the layered interconnect structure in the semiconductordevice of this embodiment comprises an insulating film 2 of, forexample, silicon oxide as formed on a silicon substrate 1, in which afirst layered interconnect structure 6 composed of a neighboring film 3,a conductor film 4 and a neighboring film 5 is connected with thesubstrate 1 via a contact hole as formed through the insulating film 2.In this, an insulating film 7 of, for example, silicon oxide is formedon the first layered interconnect structure 6, and a via 8 of, forexample, tungsten (W) is filled in the via hole as formed through theinsulating film 7. Through this via 8, a second layered interconnectstructure 12 composed of a neighboring film 9, a conductor film 10 and aneighboring film 11 is connected with the first layered interconnectstructure 6. The first layered interconnect structure 6 is characterizedin that the neighboring film 3, the conductor film 4 and the neighboringfilm 5 are formed of a combination of materials satisfying an inequalityof {A+B×(a_(p)/b_(p))}<13, where A indicates the difference between theshort side, a_(p), of the rectangular unit cells that constitute theplane with minimum free energy of the conductor film 4 and the shortside, a_(n), of the rectangular unit cells that constitute the planewith minimum free energy of the neighboring films 3, 5, and isrepresented as {|a_(p)−a_(n)|/a_(p)}×100=A (%):, and B indicates thedifference between the long side, b_(p), of the rectangular unit cellsthat constitute the plane with minimum free energy of the conduct orfilm 4 and the long side, b_(n), of the rectangular unit cells thatconstitute the plane with minimum free energy of the neighboring films3, 5, and is represented as {|b_(p)−b_(n)|/b_(p)}×100=B (%). Concretely,where the conductor film 4 is a copper (Cu) film, the neighboring films3, 5 could be any of a rhodium (Rh) film, a ruthenium (Ru) film, aniridium (Ir) film, an osmium (Os) film and a platinum (Pt) film. Wherethe conductor film 4 is a platinum (Pt) film, the neighboring films 3, 5could be any of a rhodium (Rh) film, a ruthenium (Ru) film, an iridium(Ir) film and an osmium (Os) film.

Like this, the second layered interconnect structure 12 is characterizedin that the neighboring film 9, the conductor film 10 and theneighboring film 11 are formed of a combination of materials satisfyingan inequality of {A+B×(a_(p)/b_(p))}<13, where A indicates thedifference between the short side, a_(p), of the rectangular unit cellsthat constitute the plane with minimum free energy of the conductor film10 and the short side, a_(n), of the rectangular unit cells thatconstitute the plane with minimum free energy of the neighboring films9, 11, and is represented as {|a_(p)−a_(n)|/a_(p)}×100=A (%), and Bindicates the difference between the long side, b_(p), of therectangular unit cells that constitute the plane with minimum freeenergy of the conductor film 10 and the long side, b_(n), of therectangular unit cells that constitute the plane with minimum freeenergy if the neighboring films 9, 11, and is represented as{|b_(p)−b_(n)|/b_(p)}×100=B (%). Concretely, where the conductor film 10is a copper (Cu) film, the neighboring films 9, 11 could be any of arhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir) film, anosmium (Os) film and a platinum (Pt) film. Where the conductor film 10is a platinum (Pt) film, the neighboring films 9, 11 could be any of arhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir) film and anosmium (Os) film.

The effect of the semiconductor device of this embodiment is describedbelow.

We, the inventors have specifically noticed the difference between theconductor film and the neighboring film in the short side, a, and thelong side, b, of the rectangular unit cells that constitute the planewith minimum free energy of those films, and investigated the influenceof this difference on the diffusion coefficient of the conductor filmthrough computer simulation. Concretely, for the layered interconnectstructure comprising a conductor film and a neighboring film as solayered that the two are in contact with each other, prepared was a mapwhere the abscissa indicates the difference between the short side,a_(p), of the rectangular unit cells that constitute the plane withminimum free energy of the conductor film and the short side, a_(n), ofthe rectangular unit cells that constitute the plane with minimum freeenergy of the neighboring film, {|a_(p)−a_(n)|/a_(p)}×100=A (%), and theordinaate indicates the difference between the long side, b_(p), of therectangular unit cells that constitute the plane with minimum freeenergy of the conductor film and the long side, b_(n), of therectangular unit cells that constitute the plane with minimum freeenergy of the neighboring film, {|b_(p)−b_(n)|/b_(p)}×100=B (%), asmultiplied by (a_(p)/b_(p)). Based on the data of A and B as defined tocover the map, the value of the diffusion coefficient of the conductorfilm was calculated through computer simulation.

First conducted was the simulation for a conductor film of copper (Cu)at a temperature of 700K. Copper (Cu) has the face centered cubic (fcc)structure, and the plane with minimum free energy of copper (Cu) is the(111) plane. The simulation data of this case are shown in FIG. 2, inwhich the diffusion coefficient of the copper (Cu) film greatlyincreases in the upper region as separated by the boundary line. In thelower region as separated by the boundary line, which is near to theorigin of the coordinate axes, the diffusion coefficient is small andvoids are hardly formed, while in the upper region as separated by it,the diffusion coefficient is large and voids are easily formed. To checkthis aspect in detail, the diffusion coefficient of the copper (Cu) filmwas investigated along the dotted line in FIG. 2, and the data are shownin FIG. 3. In FIG. 3, D indicates the diffusion coefficient of thecopper (Cu) film, and D₀ indicates the diffusion coefficient of, copper(Cu) in bulk. In this, it is known that the diffusion coefficientgreatly increases in the right hand region as separated by the boundaryline, in which titanium nitride (TiN) and others used in conventionalneighboring films are positioned. Referring back to FIG. 2, it is knownthat the tungsten (W) film and the tantalum (Ta) film are also in theupper region above the boundary line. On the other hand, in FIG. 2, therhodium (Rh) film, the ruthenium (Ru) film, the iridium (Ir) film, theosmium (Os) film and the platinum (Pt) film are all positioned in thelower region below the boundary line, or that is, in the region near tothe origin of the coordinate axes, and it is known that these films areeffective for preventing the copper (Cu) film from diffusion. Thematerials of those films are all within the region in which both A andB×(a_(p)/b_(p)) are smaller than 13%. Linear approximation to theboundary line in FIG. 2 gives {A+B×(a_(p)/b_(p))}<13. Therefore, in thestructure composed of a conductor film and a neighboring film as formedof a combination of materials that satisfies the inequality of{A+B×(a_(p)/b_(p))}<13, copper diffusion is retarded and voids andinterconnect breakdowns are thereby prevented. In this, the diffusioncoefficient of the copper (Cu) film is specifically noticed and it isjudged that voids are hardly formed in the copper (Cu) film with asmaller diffusion coefficient. Also in neighboring films, it is desiredthat the voids are hardly formed. For this, it is more desirable thatthe neighboring films are made of a material having a high meltingpoint. For example, more preferred for the neighboring films are rhodium(having a melting point of 1,960° C.), ruthenium (having a melting pointof 2,310°C.), iridium (having a melting point of 2,443° C.) and osmium(having a melting point of 3,045° C.) to platinum (having a meltingpoint of 1,769° C.), since the melting point of the former is all higherthan that of platinum.

Next conducted was the simulation for a conductor film of platinum (Pt).Like copper (Cu), platinum (Pt) has the face-centered cubic (fcc)structure, and the plane with minimum free energy of platinum (Pt) isthe (111) plane. The simulation data of this case are shown in FIGS. 4and 5. The same as in FIG. 2 shall apply to the data in FIG. 4. Also inFIG. 4, in the lower region as separated by the boundary line, which isnear to the origin of the coordinate axes, the diffusion coefficient issmall and voids are hardly formed, while in the upper region asseparated by it, the diffusion coefficient is large and voids are easilyformed. To check this aspect in detail, the diffusion coefficient of theplatinum (Pt) film was investigated along the dotted line in FIG. 4, andthe data are shown in FIG. 5. In FIG. 5, D indicates the diffusioncoefficient of the platinum (Pt), film, and D₀ indicates the diffusioncoefficient of platinum (Pt) in bulk. In this, it is known that thediffusion coefficient greatly increases in the right hand region asseparated by the boundary line, Referring back to FIG. 4, it is knownthat the rhodium (Rh) film, the ruthenium (Ru) film, the iridium (Ir)film and the osmium (Os) film are all positioned in the lower regionbelow the boundary line. This means that the materials for these filmsare effective for preventing the platinum (Pt) film from diffusion.Those materials are all within the region in which both A andB×(a_(p)/b_(p)) are smaller than 13%. It is understood that the positionof the boundary line in FIG. 4 well corresponds to that of the boundaryline for the copper (Cu) film noted above. Linear approximation to thoseboundary lines gives {A+B×(a_(p)/b_(p))}<13. Therefore, in the structurecomposed of a conductor film and a neighboring film as formed of acombination of materials that satisfies the inequality of{A+B×(a_(p)/b_(p))}<13, conductor film diffusion is retarded and voidsand interconnect breakdowns are thereby prevented.

Next referred to is FIG. 7 which shows a cross-sectional structure of alayered interconnect structure part of a semiconductor device of thesecond embodiment of the invention.

As in FIG. 7, the layered interconnect structure in the semiconductordevice of this embodiment comprises an insulating film 2 of, forexample, silicon oxide as formed on a silicon substrate 1, in which afirst layered interconnect structure 6 composed of a diffusion barrier13, a neighboring film 3, a conductor film 4, a neighboring film 5 and adiffusion barrier 14 is connected with the substrate 1 via a contacthole as formed through the insulating film 2. In this, an insulatingfilm 7 of, for example, silicon oxide is formed on the first layeredinterconnect structure 6, and a via 8 of, for example, tungsten (W) isfilled in the via hole as formed through the insulating film 7. Throughthis via 8, a second layered interconnect structure 12 composed of adiffusion barrier 15, a neighboring film 9, a conductor film 10, aneighboring film 11 and a diffusion barrier 16 is connected with thefirst layered interconnect structure 6. The diffusion barriers 13, 14,15, 16 comprise, for example, titanium nitride (TiN), tungsten (W),tantalum (Ta) or the like. The first layered interconnect structure 6 ischaracterized in that the neighboring film 3, the conductor film 4 andthe neighboring film 5 are formed of a combination of materialssatisfying an inequality of {A+B×(a_(p)/b_(p))}<13, where A indicatesthe difference between the short side, a_(p), of the rectangular unitcells that constitute the plane with minimum free energy of theconductor film 4 and the short side, a_(n), of the rectangular unitcells that constitute the plane with minimum free energy of theneighboring films 3, 5, and is represented as{|a_(p)−a_(n)|/a_(p)}×100=A (%), and B indicates the difference betweenthe long side, b_(p), of the rectangular unit cells that constitute theplane with minimum free energy of the conductor film 4 and the longside, b_(n), of the rectangular unit cells that constitute the planewith minimum free energy of the neighboring films 3, 5, and isrepresented as {|b_(p)−b_(n)|/b_(p)}×100=(%). Concretely, where theconductor film 4 is a copper (Cu) film, the neighboring films 3, 5 couldbe any of a rhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir)film, an osmium (Os) film and a platinum (Pt) film. Where the conductorfilm 4 is a platinum (Pt) film, the neighboring films 3, 5 could be anyof a rhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir) film andan osmium (Os) film.

Like this, the second layered interconnect structure 12 is characterizedin that the neighboring film 9, the conductor film 10 and theneighboring film 11 are formed of a combination of materials satisfyingan inequality of {A+B×(a_(p)/b_(p))}<13, where A indicates thedifference between the short side, a_(p), of the rectangular unit cellsthat constitute the plane with minimum free energy of the conductor film10 and the short side, a_(n), of the rectangular unit cells thatconstitute the plane with minimum free energy of the neighboring films9, 11, and is represented as {|a_(p)−a_(n)|/a_(p)}×100=A (%), and Bindicates the difference between the long side, b_(p), of therectangular unit cells that constitute the plane with minimum freeenergy of the conductor film 10 and the long side, b_(n), of therectangular unit cells that constitute the plane with minimum freeenergy of the neighboring films 9, 11, and is represented as{|b_(p)−b_(n)|/b_(p)}×100=B (%). Concretely, where the conductor film 10is a copper (Cu) film, the neighboring films 9, 11 could be any ofrhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir) film, anosmium (Os) film and a platinum (Pt) film. Where the conductor film 10is a platinum (Pt) film, the neighboring films 9, 11 could be any of arhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir) film and anosmium (Os) film.

Next referred to is FIG. 8 which shows a cross-sectional structure of aprincipal part of a semiconductor device of the third embodiment of theinvention. As in FIG. 8, the semiconductor device of this embodimentcomprises diffusion layers 102, 103, 104, 105 all formed on a siliconsubstrate 101, on which are formed gate insulating films 106, 107 andgate electrodes 108, 109 to construct MOS transistors. Thegate-insulating films 106, 107 are, for example, silicon oxide films orsilicon nitride films; and the gate electrodes 108, 109 are, forexample, polycrystalline silicon films, thin metal films or metalsilicide films, or are of a layered structure comprising any of them.The MOS transistors are separated from each other by an isolation film110 of, for example, a silicon oxide film. The gate electrodes 108, 109are covered with insulating films 111, 112, respectively, of, forexample, silicon oxide films, entirely on their top and side surfaces.The MOS transistors are entirely covered with an insulating film 113,which may be, for example, a BPSG (boron-doped phosphosilicate glass) orSOG (spin on glass) film or with a silicon oxide or nitride film asformed through chemical vapor deposition (CVD) or physical vapordeposition (PVD). In each contact hole as formed through the insulatingfilm 113, formed is a plug of a conductor film 115 which is in contactwith neighboring films 114 a, 114 b of diffusion barriers. The plugs areconnected with the diffusion layers 102, 103, 104, 105. Via the plugs,the diffusion layers are connected with a layered interconnect thatcomprises a conductor film 117 as coated with neighboring films 116 a,116 b of diffusion barriers. The layered interconnect is formed, forexample, by forming trenches for interconnection in an insulating film118, then forming a neighboring film 116 a at the bottom of each trench,forming a conductor film 117 on the film 116 a, and further forming aneighboring film 116 b on the film 117. When the neighboring films 116a, 116 b of diffusion barriers and the conductor film 117 are formed, atleast one of those films 116 a, 116 b and 117 is formed at least throughphysical vapor deposition (PVD) as in the ordinary manner. Where theconductor film 117 is formed through physical vapor deposition, it maybe formed first through physical vapor deposition such as sputtering orthe like in some degree, and thereafter according to a differentfilm-forming method (of, for example, plating or chemical vapordeposition that is favorable to film formation it narrow trenches) as inthe ordinary manner. Electromigration resistance is especially importantfor the case of switching film-forming methods. Without switching tosuch a different film-forming method, the physical vapor deposition maybe continued to finish the film 117. On the film 117, formed is a plugof a conductor film 120. For this, a via hole is formed through aninsulating film 121 having been formed on the film 118, and theconductor film 120 coated with neighboring films 119 a, 119 b ofdiffusion barriers is formed in the via hole. The plug is thus connectedwith the layered interconnect formed previously. Via the plug, a secondlayered interconnect that comprises a conductor film 123 as coated withneighboring films 122 a, 122 b of diffusion barriers is connected withthe conductor film 117. The second layered interconnect is formed, forexample, by forming trenches for interconnection in an insulating film124, then forming the neighboring film 122 a at the bottom of eachtrench, for example through chemical vapor deposition, forming theconductor film 123 on the film 122 a, and further forming theneighboring film 122 b on the film 123, for example, through chemicalvapor deposition. The second layered interconnect may be formed beforethe insulating film 124 is formed. The conductor film 123 may be formedfirst through physical vapor deposition in some degree, and thereafteraccording to a different film-forming method (of, for example, platingor chemical vapor deposition). For forming the plug of the conductorfilm 120 as coated with the neighboring films 119 a, 119 b, and thesecond layered interconnect, another process may be employed whichcomprises forming trenches in the insulating films 121, 124, thenforming the neighboring films 119 a, 119 b and the neighboring film 122a all at a time, and thereafter forming the conductor film 120 and theconductor film 123. An insulating film 125 is, for example, a siliconoxide film.

In the third embodiment, at least one of the conductor film 117 ascoated with the neighboring films 116 a, 116 b, and the conductor film123 as coated with the neighboring films 122 a, 122 b shall be formed ofa combination of materials that satisfies an inequality of{A+B×(a_(p)/b_(p))}<13, where A indicates the difference between theshort side, a_(n), of the rectangular unit cells that constitute theplane with minimum free energy of the neighboring films and the shortside, a_(p), of the rectangular unit cells that constitute the planewith minimum free energy of the conductor film, and is represented as{|a_(p)−a_(n)|/a_(p)}×100=A (%), and B indicates the difference betweenthe long side, b_(n), of the rectangular unit cells that constitute theplane with minimum free energy of the neighboring films and the longside, b_(p), of the rectangular unit cells that constitute the planewith minimum free energy of the conductor film, and is represented as{|a_(b)−b_(n)|/b_(p)}×100=B (%). This is for the purpose of retardingthe diffusion of the conduct film so as to prevent voids that may becaused by so called electromigration. Concretely, for example, where theconductor film 117 is a copper (Cu,) film, the neighboring films 116 a,116 b could be any one selected from the group consisting of a rhodium(Rh) film, a ruthenium (Ru) film, an iridium (Ir) film, an osmium (Os)film and a platinum (Pt) film. Since the conductor films 115, 120 forthe plugs are adjacent to the conductor film 117, they could beconsidered as the neighboring films to the conductor film 117.Therefore, where the conductor film 117 is a copper (Cu) film, the plugs115, 120 could be any one selected from the group consisting of arhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir) film, anosmium (Os) film and a platinum (Pt) film, by which the diffusion of theconductor film 117 is retarded to prevent voids that may be caused byso-called electromigration. In that constitution, since the rhodium (Rh)film, the ruthenium (Ru) film, the iridium (Ir) film, the osmium (Os)film and the platinum (Pt) film for the plug all have a higher meltingpoint than a copper (Cu) film, the plug could exhibit an additionaleffect of such that its resistance against heat is higher than that ofplugs of conductor films 115, 120 of being copper (Cu) films. In thiscase, it is desirable that the neighboring films 114 a, 114 b, 119 a,119 b to be adjacent to the conductor films 115, 120 are titaniumnitride (TiN) films, as exhibiting good adhesiveness to the insulatingfilms 113, 121. If the adhesiveness between them could be neglected, theneighboring films 114 a, 114 b, 119 a, 119 b may be omitted. Where thelow level of electric resistance of the plug is regarded as moreimportant than the resistance thereof against heat, a copper (Cu) filmis used for the conductor films 115, 120 for the plug, and any oneselected from the group consisting of a rhodium (Rd) film, a ruthenium(Ru) film, an iridium (Ir) film, an osmium (Os) film and a platinum (Pt)film is used for the neighboring films 114 a, 114 b, 119 a, 119 badjacent to the conductor films 115, 120. Though not shown in FIG. 8,any one or more additional layers may be formed between each of theneighboring films 116 a, 116 b, 122 a, 122 b, 114 a, 114 b, 119 a, 119 band the insulating film adjacent thereto, as in FIG. 7.

Though not in FIG. 8, it is desirable to provide a diffusion barrieralso on the side walls of the conductor film 117 and the conductor film123, in order to prevent atoms from diffusing into the insulating filmsthrough the side walls of the conductor films 117, 123.

The invention is not limited to only interconnects, diffusion barriersand plugs, but could apply to electrodes.

For example, where the gate electrodes 108, 109 have a layered structurethat comprises a conductor film and a neighboring film, they may beformed of a combination of materials that satisfies an inequality of{A+B×(a_(p)/b_(p))}<13, in which A indicates the difference between theshort side, a_(n), of the rectangular unit cells that constitute theplane with minimum free energy of the neighboring film and the shortside, a_(p), of the rectangular unit cells that constitute the planewith minimum free energy of the conductor film, and is represented as{|a_(p)−a_(n)|/a_(p)}×100=A (%), and B indicates the difference betweenthe long side, b_(n), of the rectangular unit cells that constitute theplane with minimum free energy of the neighboring film and the longside, b_(p), of the rectangular unit cells that constitute the planewith minimum free energy of the conductor film, and is represented as{|b_(p)−b_(n)|/b_(p)}×100=B (%). This is for the purpose of retardingthe diffusion of the conductor film sc as to prevent voids that may becaused by so-called electromigration. Concretely, for example, where theconductor film is a copper (Cu) film, the neighboring film could be anyone selected from the group consisting of a rhodium (Rh) film, aruthenium (Ru) film, an iridium (Ir) film, an osmium (Os) film and aplatinum (Pt) film. Where the conductor film is a platinum (Pt) film,the neighboring film could be any one selected from the group consistingof a rhodium (Rh) film, a ruthenium (Ru) film, an iridium (Ir) film andan osmium (Os) film. If desired, an additional film of titanium nitrideor the like may be provided between the gate electrodes 108, 109 and thegate insulating films 106, 107.

In the embodiments mentioned above, where a copper (Cu) film is used forthe conductor film, any one selected from the group consisting of arhodium (Rh) film, a ruthenium (Ru) film, an iridium, (Ir) film, anosmium (Os) film and a platinum (Pt) film is used for the neighboringfilm for retarding the copper diffusion. Of those, a ruthenium (Ru) filmwill be the best for the neighboring film, as having a high meltingpoint and being easy to work.

FIG. 9 is referred to, which shows one preferred functional structure ofthe semiconductor device of the third embodiment. The structuraldifference between FIG. 9 and FIG. 8 is that, in FIG. 9, a neighboringfilm 126 a is formed between the neighboring film 116 a and theinsulating film 113, a neighboring film 126 b is formed between theneighboring film 116 b and the insulating film 121, a neighboring film127 a is formed between the neighboring film 122 a and the insulatingfilm 121, and a neighboring film 127 b is formed between the neighboringfilm 122 b and the insulating film 121. The conductor films 117, 123 tobe interconnects are copper (Cu) films having a low electric resistance,in order that the device could have good capabilities for rapidoperation. In order to make the copper (Cu) film interconnects have goodelectromigration resistance, the neighboring films 116 a, 116 b, 122 a,122 b of diffusion barriers for the copper (Cu) films 117, 123 areruthenium (Ru) films. The plugs 115, 120 adjacent to the copper (Cu)films 117, 123 are ruthenium (Ru) films so as to have goodelectromigration resistance. Electromigration resistance is especiallyimportant near plugs, for example, as in “Materials Reliability inMicroelectronics”, pp. 81-86 in Vol. 428 of Symposium Proceedings of theMaterials Research Society (MRS). The ruthenium (Ru) plugs have theadvantage of good resistance against heat. In that constitution, theplug 115 and the diffusion barrier 116 a are both ruthenium (Ru) films,and it is desirable to form these films both at a time as facilitatingthe film formation. Like those, the plug 120 and the diffusion barrier127 a are also both ruthenium (Ru) films, and it is desirable to formthese films both at a time as facilitating the film formation. In orderto enhance the adhesiveness between the ruthenium (Ru) films and theinsulating films adjacent thereto, the diffusion barriers 126 a, 126 b,127 a, 127 b, 114 a, 114 b, 119 a, 119 b all are of a titanium nitride(TiN) film. In that constitution, the diffusion barriers 114 a, 114 band the diffusion barrier 126 a are all titanium nitride (TiN) films,and it is desirable to form these films all at a time as facilitatingthe film formation. Like those, the diffusion barriers 119 a, 119 b andthe diffusion barrier 127 a are all titanium nitride (TiN) films, and itis desirable to form these films all at a time as facilitating the filmformation. Of those, at least one of the copper films and the diffusionbarriers is formed at least through sputtering. It is more desirablethat a film with low contact resistance, such as a metal silicide filmor the like, is provided between the diffusion barrier 114 a and thediffusion layer 104.

Though not shown in FIG. 9, it is more desirable to additionally form adiffusion barrier on the side walls of the copper (Cu) film 117 and thecopper (Cu) film 123 thereby preventing copper (Cu) atoms from diffusinginto the insulating films from the side walls of the copper (Cu) film117 and the copper (Cu) film 123.

The data of computer simulation shown in FIGS. 2, 3, 4 and 5 are thoseof molecular dynamics simulation. Molecular dynamics simulation is for amethod of calculating the position of each atom at varying times bycomputing the force acting on each atom through interatomic potentialfollowed by solving the Newton's equation of motion on the basis of thatforce, for example, as in Journal of Applied Physics, Vol. 54 (1983),pp. 4864-4878. A method for calculating a diffusion coefficient of asubstance through molecular dynamics simulation is described, forexample, in Physical Review B, Vol. 29 (1984), pp. 5363-5371. It is wellknown that reducing copper (Cu) diffusion improves the electromigrationresistance of copper (Cu) films, for example, as in “MaterialsReliability in Microelectronics”, pp. 43-60 in Vol. 428 of SymposiumProceedings of the Materials Research Society (MRS). As so mentionedhereinabove, FIGS. 2, 3, 4 and 5 show the simulation data obtainedherein at a temperature or 700K, and the same effects could be shownunder different simulation conditions including different temperatures,etc.

FIG. 6 shows rectangular unit cells that constitutes the crystal planewith minimum free energy in a bulk crystal, in which the short side, a,and the long side, b, of the rectangular unit cell are defined. This isdescribed in more detail hereinunder. The short side, a, indicates theinteratomic distance between the nearest neighbors in a bulk crystal,which is referred to, for example, in a Japanese translation ofIntroduction to Solid Stage Physics, Part I, 5th Ed. (written by CharlesKittel, published by Maruzen in 1978), page 28. The long side, b, isabout 1.73 times the short side, a, in crystals with the face-centeredcubic structure or the hexagonal close-packed structure, but is about1.41 times the short side, a, in crystals with the body-centered cubicstructure. For example, the plane with minimum free energy of copper(Cu) having the face-centered cubic structure is the (111) plane, andits short side, a_(Cu), is about 0.26 nm, while its long side, b_(Cu),is about 0.44 nm. The plane with minimum free energy of ruthenium (Ru)having the hexagonal close-packed structure is the (001) plane, and itsshort side, a_(Ru), is about 0.27 nm, while its long side, b_(Ru), isabout 0.46 nm.

Based on “the results of the invention as above, we, the inventors havemade researches about related techniques. As a result, we have foundJP-A-10-229084 relating to copper (Cu) interconnects and diffusionbarriers for them. However, this obviously differs from the presentinvention for the following reasons. Specifically, JP-A-10-229084 isdirected to a technical theme for easy formation of a diffusion barrierand a copper (Cu) film interconnect in contact holes having a highaspect ratio, and its subject matter is to construct an interconnectstructure by forming both the diffusion barrier and the copper (Cu) filminterconnect through plating or chemical vapor deposition (CVD) but notthrough physical vapor deposition (PVD) such as sputtering or the like.Being different from this, the present invention is directed to aninterconnect structure for which at least one of a diffusion barrier anda copper (Cu) film interconnect is formed through physical vapordeposition, like those for ordinary interconnect structures. The subjectmatter of the present invention is to improve the electromigrationresistance, which is especially important for films formed throughphysical vapor deposition. For an ordinary diffusion barrier and acopper (Cu) film interconnect, at least one of them is formed throughphysical vapor deposition such as sputtering or the like, for example,as in a monthly journal, Semiconductor World(for February 1998, pp.91-96, published by Press Journal). As so described therein, for forminga copper (Cu) film interconnect through plating or chemical vapordeposition (CVD), generally employed is a method comprising previouslyforming a seed layer for a copper (Cu) film through physical vapordeposition (PVD) such as sputtering or the like, which is then switchedto plating or chemical vapor deposition (CVD) to complete the intendedcopper (Cu) film interconnect. Therefore, the method proposed inJP-a-10-229084, in which both a diffusion barrier and a copper (Cu) filminterconnect are formed through plating or chemical vapor deposition(CVD) but not through physical vapor deposition (PVD) such as plating orthe like, will be favorable to the object for forming: them in contactholes having a high aspect ratio, but, at present, the method isscarcely put into practical use The reason is, as so described, forexample, in the monthly journal, Semiconductor World (for February 1998,pp. 86-96, published by Press Journal), because the seed layer for acopper (Cu) film as formed through physical vapor deposition (PVD) hasbetter adhesiveness than that formed through chemical vapor deposition(CVD), because direct plating of a copper (Cu) film on a diffusionbarrier is almost impossible, and because the diffusion barrier formedthrough chemical vapor deposition (CVD) has the disadvantage of eitherhigh electric resistance or poor barrier capabilities. Sputtering ismost popularly employed for physical vapor deposition (PVD), for whichis used a rare gas element (this may be referred to as a noble gaselement, such as argon (Ar), xenon (Xe), krvoton (Kr), neon Ne) or thelike, for example, as in Thin Film Handbook (published by Ohm Sha, Ltd.,edited by the Japan Society for the Promotion of Science), pp. 171-196.Therefore, films as formed through sputtering shall inevitably containthe rare gas element used, in an amount of at least 0.0001%, but arepreferred to those formed through plating or chemical vapor deposition(CVD) as having better adhesiveness than the latter.

Naturally, the terminology, diffusion barrier as referred to herein ismeant to be a film for preventing the diffusion of an interconnectmaterial such as copper (Cu) or the like. For example, the neighboringfilms 116 a, 116 b as provided adjacent to the conductor film 117 ofcopper (Cu) are diffusion barriers. However, the diffusion barrier mayact for improving adhesiveness, or for controlling crystal orientationor even for controlling grain size, and, as the case may be, its primaryrole is often not for diffusion retardation. In the presentspecification, the neighboring films with conductivity, such as 116 a,116 b, 114 a, 114 b that are provided adjacent to conductor films areall referred to as diffusion barriers, even though they act for otherobjects but not for diffusion retardation only.

The copper (Cu) film referred to herein indicates a film for which theprimary constituent element is copper (Cu), and it may additionallycontain any other elements. With such other elements, the film couldstill exhibit the same effects as herein. The same shall apply to theruthenium (Ru) film and others referred to therein.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A semiconductor device, comprising a copper film formed on oneprimary surface of a semiconductor substrate, and a neighboring filmformed in contact with said copper film, wherein said neighboring filmis a ruthenium film and the (111) plane of said copper film which hasthe face centered cubic structure contacts with the (001) plane of saidruthenium film which has the hexagonal close-packed structured.